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LAYERS OF ATMOSPHERE AND
VARIOUS REACTIONS IN IT
Handled by: Atun RoyChoudhuryDiscipline: Environmental
Semester: 1st
Vertical distribution of atmospheric layers:
Direct interaction of UV rays with earth surface:
Important Atmospheric Chemical Species:
Inorganic oxides: CO, CO2, NO2, SO2
Oxidants: O3, H2O2, HO• radical, HO2• radical, ROO• radicals, NO3 radical Reductants: CO, SO2, H2S Hydrocarbons: Natural CH4, pollutant alkanes, alkenes, aromatics Oxidized organics: Aldehydes, ketones, acids, organic nitrates Photochemically active species: NO2, formaldehyde Acids: H2SO4, H2SO3, HNO3
Bases: NH3
Salts: NH4HSO4
Unstable reactive species: Electronically excited nitrogen dioxide (NO2*), HO•
Solid and liquid particles in aerosols and clouds Sources and sinks for gas-phase species Sites for surface reactions on solids Aqueous phase reactions in water droplets
Important aspects of atmospheric chemical processes:
Two Very Important Factors in Atmospheric Chemistry:
(i) Radiant solar energy Photons put high energy into individual molecules
(ii) Hydroxyl radical, HO• Most important highly reactive intermediate
Loss of Excitation Energy from Electronically Excited Species:
(i) Emission of a photon (light): NO2* NO2 + h
Called luminescence if instantaneous, phosphorescence if slower andChemiluminescence when the excited species that emits a photon is
formed as the result of a chemical reactionO3 + NO O2 + NO2* (luminescent species)
(ii) Direct reaction of an excited speciesO2* + O3 2O2 + O
(iii) DissociationNO2* NO + O (very important tropospheric reaction)
O2* O + O (important in stratosphere leading to O3)
(iv) Photoionization (formation of ions in the ionsphere)N2* N2
+ + e-
Photochemical Reaction:
Photochemical cycle:
Basic elements of SMOG:
Photochemical smog generation:
Pictorial representation of Smog:
Basics of Photochemical reaction:
Other important compound:
Beijing location showing smog effect:
Introduction of Ozone: O3 a gas composed of three atoms of
oxygen bluish gas that is harmful to breathe Nearly 90% of the Earth's ozone is in the
stratosphere and is referred to as the ozone layer
Ozone absorbs a band of ultraviolet radiation called UVB
Formation of Ozone:
Ozone depleting substances:
CFCs, HCFCs, halons, methyl bromide, carbon tetrachloride, and methyl chloroform.
Anthropogenic activities causing depletion of Ozone:
Study of Ozone layer with respect to time:
Effects of ozone layer depletion: